Structural composites are well known and are used in a wide variety of applications that require plastic parts having a minimum threshold of mechanical properties such as strength and impact resistance while imparting cost savings in terms of manufacturing techniques and in terms of weight reduction. Examples of structural composites include sheet molding compound (SMC) and structural reaction injection molding (SRIM).
Structural composites are typically made by introducing glass fiber or other reinforcing material to a thermoplastic or thermosetting polymer material. The glass fiber and polymer material may be mixed together and formed into a composite part in a wide variety of methods, including compression molding and injection molding. Examples of structural composites include sheet molding compound (SMC) and structural reaction injection molding (SRIM).
Many problems exist with the technologies used to make structural composites and are inherent in the structural composites themselves. First, the thermoplastic or thermosetting polymer materials commonly used in these processes are typically solvent-based systems. As such, volatile organic content (VOC) may be released to the atmosphere as the part is cured. Second, the process used to make the material is very complicated, thus adding to the manufacturing costs. For example, in a typical SRIM process, the reinforcement materials and polymer resin are introduced individually to the molding equipment and the part is molded, which adds to the cost of manufacture. Third, in these types of equipment, composite parts having an inadequately dispersed reinforcement material in the part is possible if the machine is calibrated inappropriately. Finally, in injection molding processes, the amount of fiber content that may be loaded within the composite part is limited due to the process itself as is well known in the art. As polymer resins are typically more expensive than the reinforcement material, the cost of the composite part is correspondingly increased.
With regard to the VOC problem one potential polymer system that may be used is a powder coating system. Powder coating systems use aqueous slurries of polymer powder and water to introduce coatings to a part. Organic emissions are limited to additives that may help the polymer remain dispersed in the slurry and to help the resin flow during the curing step.
It is therefore highly desirable to provide a method for combining the powder coating industry and glass fiber industry for making structural composite parts. It is also desirable to increase the fiber content in structural composite parts to improve or maintain mechanical properties such as strength or impact resistance. It is also desirable to simplify the manufacturing of structural composite parts by introducing the polymer resin and fiber reinforcement material in one step to be molded to a desired shape.